Process for the carbonylation of an ethylenically unsaturated compound and catalyst therefore

ABSTRACT

A process for the carbonylation of an ethylenically unsaturated compound with carbon monoxide and a co-reactant. The carbonylation reaction is carried out in the presence of a novel catalyst involving: a) a source of a group VIII metal; 
 
b) a bidentate diphosphine of formula I,  
                 
 
wherein R 1  represents a bivalent radical that together with the phosphorus atom to which it is attached is an optionally substituted 2-phospha-tricyclo[3.3.1.1{3,7}]-decyl group or a derivative thereof in which one or more of the carbon atoms are replaced by heteroatoms (“2-PA” group); wherein R 2  and R 3  independently represent univalent radicals of up to 20 atoms or jointly form a bivalent radical of up to 20 atoms; and wherein A 1  and A 2  independently represent optionally substituted alkylene groups and R represents an optionally substituted aromatic group; and, 
c) a source of anions.

The present invention relates to a process for the carbonylation of anethylenically unsaturated compound with carbon monoxide and aco-reactant and a catalyst therefore. More specifically the presentinvention relates to a process for the preparation of a carboxylic acid,especially propanoic acid, or a derivative thereof by reaction of ethenewith carbon monoxide and water or another appropriate co-reactant.

WO-A-9842717 relates to the carbonylation of unsaturated compounds. Inexample 3 it describes the preparation of propanoic acid by reactingethene with water in the presence of a catalyst comprising 0.1 mmol ofpalladium (II) acetate, 0.15 mmol of1,3-PP′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl)propane and 0.2 mmol methyl sulphonic acid. Ethene was fully convertedwith 100% selectivity into propanoic acid at an average rate of 1500mol/mol.hr.

WO-A-0172697 relates to the carbonylation of pentenenitrile to preparecyanovaleric acid in the presence of a catalyst comprising a specificbidentate phosphine, arsine or stibine ligand. In this bidentate ligandthe P, As or Sb atoms are connected via an organic bridging group andeach substituted with two tertiary alkyl groups.

In the description a broad variety of possible bridging groups arementioned. Although, in passing, divalent aryl groups, viz. dixylyl, arementioned, preference is given to C₃-C₅ alkylene groups.

Furthermore a broad variety of possible tertiary alkyl groups arementioned. In passing, it is mentioned that the tertiary alkyl groupsinclude cyclic structures, viz. an alkyl substituted 2-phosphatricyclo[3.3.1.1{3,7}]decyl group. Preference, however, is given to bidentatediphosphines containing non-cyclic tertiary alkyl groups, such astert.-butyl groups. These preferences are confirmed in the examples. Theuse of a catalyst comprising 1,3-bis (di-tert.-butylphosphino) propaneas a ligand, viz. example 3 and 8, results in a higher reaction rate andconversion than the use of a catalyst comprising 1,2-bis(di-tert.-butylphosphinomethyl) benzene as a ligand, viz. example 9.Furthermore the use of a catalyst comprising 1,3-bis(di-tert-butylphosphino) propane as a ligand, viz. example 1, results ina higher reaction rate and conversion than the use of a catalystcomprising1,3-PP′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl)propane as a ligand, viz. example 10.

WO-A-0185662 relates to a process for producing aldehydes byhydroformylation of a vinyl-group containing compound. The object of theinvention was to obtain a high selectivity towards the normal product.The hydroformylation reaction is carried out in the presence of acatalyst comprising a group VIII metal and a diphosphine ligandcontaining two 2-phospha-tricyclo[3.3.1.1{3.7}]-decyl groups connectedby a bridge X. A wide range of possible bridges are indicated by theirgeneric formulae. However, only diphosphine ligands having a “ethane”,“propane” and “hexane” bridge are specifically mentioned. The examplesdisclose only the use of a catalyst containing rhodium dicarbonylacetylacetonate and1,3-PP′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]decyl)propane.

In section 3.2 of his thesis “Phospha-adamantanes a new class of bulkyalkyl phosphine ligands” (thesis submitted to the University of Bristolin April 2000), Robert Pugh describes the synthesis of1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}decyl)-o-xylene.No applications are indicated for this ligand.

Although the processes as described in WO-A-9842717 and WO-A-0172697result in more than satisfactory reaction rates, there is still room forimprovement. A process resulting in even higher reaction rates istherefore desirable.

Accordingly the present invention provides a process for thecarbonylation of an ethylenically unsaturated compound with carbonmonoxide and a co-reactant in the presence of a catalyst comprising:

-   a) a source of a group VIII metal;-   b) a bidentate diphosphine of formula I,    wherein R¹ represents a bivalent radical that together with the    phosphorus atom to which it is attached is an optionally substituted    2-phospha-tricyclo[3.3.1.1{3,7}]-decyl group or a derivative thereof    in which one or more of the carbon atoms are replaced by heteroatoms    (“2-PA” group); wherein R² and R³ independently represent univalent    radicals of up to 20 atoms or jointly form a bivalent radical of up    to 20 atoms; and wherein A¹ and A² independently represent    optionally substituted alkylene groups and R represents an    optionally substituted aromatic group; and-   c) a source of anions.

The processes of the present invention results in high reaction rates.

In the process according to the invention the ethylenically unsaturatedcompound is preferably an alkene having from 2 to 20, more preferablyfrom 2 to 10, and most preferably from 2 to 4 carbon atoms. The alkenecan be normal, branched or can comprise a cyclic structure. The alkenecan comprise one or more double bonds per molecule and those doublebonds can be internal or terminal. In the alkene one or more hydrogenatoms may have been replaced by other atoms, such as halogen atoms,sulphur atoms, oxygen atoms or nitrogen atoms, or by groups of atoms,such as hydroxyl groups; cyano groups; alkoxy groups, such as methoxy orethoxy groups; thioxy groups; amino groups such as dimethyl- anddiethyl-amino groups; or aromatic groups, such as phenyl, tolyl ornaphthyl groups. Preferably the alkene contains no heteroatoms.

Examples of alkenes include ethene, propene, 1- or 2-butene, 1- orinternal pentene, 1- or internal hexene, 1- or internal heptene, 1- orinternal octene, 1- or internal decene, internal or terminal C₁₄-C₁₈olefins, pentenenitrils, cyclohexene and styrene. Preferred alkenesinclude ethene, propene, 1-butene and 2-butene. Ethene is especiallypreferred.

In the process according to the present invention, the carbon monoxidecan be used in its pure form or diluted with an inert gas such asnitrogen, carbon dioxide or noble gases such as argon. If theethylenically unsaturated compound is a gas, e.g. ethene, a gaseousmixture of carbon monoxide and the ethylenically unsaturated compoundcan be used. If the co-reactant is hydrogen, a gaseous mixture of carbonmonoxide and hydrogen can be used.

The process according to the invention can be carried out with a widerange of co-reactants, including for example molecular hydrogen, water,monohydric alkanols, such as methanol, ethanol, isopropanol and1-butanol, and polyhydric alkanols, such as ethylene glycol,1,4-butanediol and glycerol; thiols; aromatic alkanols such as phenol;primary or secondary (poly-) amines or amides, such as diethylamine,N,N-dimethyl ethylenediamine; and carboxylic acids, for example aceticacid, pivalic acid and propanoic acid.

Of these, molecular hydrogen and hydroxyl group containing compounds,such as water, alkanols and carboxylic acids are preferred. Of these,the hydroxyl-group containing compounds are especially preferred for thepreparation of carboxylic acids and their derivatives. Preferredhydroxyl group containing compounds include water, monohydric alkanolshaving from 1 to 6 carbon atoms per molecule, such as methanol, ethanol,propanol and 1-butanol, dihydric alkanols having from 2 to 6 carbonatoms, such as ethylene glycol and 1,4-butanediol and phenol. Mostpreferably the co-reactant is water.

The process is carried out in the presence of a specific novel catalyst.The present invention therefore also relates to a catalyst comprising:

-   a) a source of a group VIII metal;-   b) a bidentate diphosphine of formula I,    wherein R¹ represents a bivalent radical that together with the    phosphorus atom to which it is attached is an optionally substituted    2-phospha-tricyclo[3.3.1.1{3,7}]-decyl group or a derivative thereof    in which one or more of the carbon atoms are replaced by heteroatoms    (“2-PA”-group); wherein R² and R³ independently represent univalent    radicals of up to 20 atoms or jointly form a bivalent radical of up    to 20 atoms; and wherein A¹ and A² independently represent    optionally substituted alkylene groups and R represents an    optionally substituted aromatic group; and-   c) a source of anions.

Examples of group VIII metals that can be used include Ru, Rh, Ni, Pdand Pt. Preferably a source of group 10 metal is used, such as Ni, Pd orPt, or group 9 metal Rhodium. Of these, palladium and platinum are morepreferred. Palladium is especially preferred.

Examples of suitable metal sources are platinum or palladium compoundssuch as salts of palladium or platinum and carboxylic acids with up to12 carbon atoms, palladium- or platinum complexes, e.g. with carbonmonoxide or acetylacetonate, or palladium or platinum combined with asolid material such as an ion exchanger. Palladium (II) acetate,palladium dibenzylacetone and platinum (II) acetylacetonate are examplesof preferred metal sources.

In the diphosphine of formula I, R represents an optionally substitutedaromatic group which is linked to the phosphorus atoms via the alkylenegroups. The aromatic group can be a monocyclic group, such as forexample a phenyl group; or a polycyclic group, such as for examplenaphthyl, anthryl or indyl group. Preferably, the aromatic group Rcontains only carbon atoms, but R can also represent an aromatic groupwherein a carbon chain is interrupted by one or more hetero atoms, suchas nitrogen, sulphur or oxygen atom in for example a pyridine, pyrrole,furan, thiophene, oxazole or thiazole group. Most preferably thearomatic group R represents a phenyl group.

Optionally the aromatic group is substituted. Suitable substituentsinclude groups containing hetero-atoms such as halides, sulphur,phosphorus, oxygen and nitrogen. Examples of such groups includechloride, bromide, iodide and groups of the general formula —O—H, —O—X²,—CO—X², —CO—O—X², —S—H, —S—X², —CO—S—X², —NH₂, —NHX², —NR²X³, —NO₂, —CN,—CO—NH₂, —CO—NHX², —CO—NX²X³ and —CI₃, in which X² and X³,independently, represent alkyl groups having from 1 to 4 carbon atomslike methyl, ethyl, propyl, isopropyl and n-butyl.

If the aromatic group is substituted it is preferably substituted withone or more aryl, alkyl or cycloalkyl groups, preferably having from 1to 10 carbon atoms. Suitable groups include, methyl, ethyl, propyl,iso-propyl, butyl and iso-butyl, phenyl and cyclohexyl. Most preferably,however, the aromatic group is non-substituted and only linked to thealkylene groups which connect it with the phosphorus atoms. Preferablythe alkylene groups are connected at adjacent positions, for example the1 and 2 positions, of the aromatic group.

Preferably the alkylene groups A¹ and A² are each independently a loweralkylene group. By a lower alkylene group is understood an alkylenegroup comprising from 1 to 4 carbon atoms. Each alkylene groups canindependently be substituted, for example with alkyl groups, ornon-substituted. Preferably the alkylene groups are bothnon-substituted. More preferably the alkylene groups are bothunsubstituted methylene or ethylene groups, most preferably methylenegroups.

R¹ in the diphosphine of formula I represents a bivalent radical thattogether with the phosphorus atom to which it is attached is anoptionally substituted 2-phospha-tricyclo[3.3.1.1{3,7}]decyl group or aderivative thereof in which one or more of the carbon atoms are replacedby heteroatoms.

Tricyclo[3.3.1.1{3,7}]decane is the systematic name for a compound moregenerally known as adamantane. Therefore, the optionally substituted2-phospha-tricyclo-[3.3.1.1{3,7}decyl group or a derivative thereof willbe referred to as “2-PA” group (as in 2-phosphadamantyl group)throughout the specification.

Preferably, the 2-PA group is substituted on one or more of the 1, 3, 5or 7 positions with a monovalent radical R⁵ of up to 20 atoms,preferably of 1 to 10 carbon atoms and more preferably of 1 to 6 carbonatoms. Examples of R⁵ include methyl, ethyl, propyl, phenyl, and4-dodecylphenyl. More preferably, the 2-PA group is substituted on eachof the 1, 3, 5 and 7 positions, suitably with identical radicals R⁵.

The 2-PA group has preferably additional heteroatoms other than the2-phosphorus atom in its skeleton. Suitable heteroatoms are oxygen andsulphur atoms. Suitably, these heteroatoms are found in the 6, 9 and 10positions.

The most preferred bivalent radical is the2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxadamantyl group.

If R² and R³ each independently represent univalent radicals of up to 20atoms, they preferably represent univalent radicals of in the range from1 to 10 carbon atoms. The univalent radicals can be aliphatic, aromaticor cycloaliphatic, and can be straight or branched. The radicals caneach independently comprise heteroatoms such as N, O and S, butpreferably comprise only carbon atoms. Examples of univalent radicalsinclude hydrocarbyl groups such as, for instance, methyl, ethyl, propyl,tert.-butyl, cyclohexyl, phenyl, pyridyl, and (substituted)trimethylsilyl or alkoxy groups. Alternatively, R² and R³ may togetherform a bivalent radical, such as 1,6-hexylene, 1, 3 or1,4-cyclooctylene. Preferably, R² and R³ together with the phosphorusatom form a 2-PA group as described herein before. Most preferably R²and R³ together with the phosphorus atom form a 2-PA group identical toR¹.

An especially preferred bidentate diphosphine is a diphosphine whereinR² and R³ together with the phosphorus atom form a 2-PA group similar,and more preferably identical, to R¹, wherein the 2-PA groups arepreferably connected by a ortho-xylyl group. Preferences for the 2-PAgroups are indicated herein above.

Most preferably the diphosphine is a compound according to Formula II,wherein R⁵ represents alkyl groups of 1 to 6 carbon atoms, preferablymethyl.

A very advantageous bidentate diphosphine in the process of the presentinvention is1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}decyl)-methylene-benzene(also sometimes referred to as1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}decyl)-ortho-xylene).

The bidentate ligands used in the process according to the invention canbe prepared as described for example by Robert Pugh in his theses“Phospha-adamantanes a new class of bulky alkyl phosphine ligands”(thesis submitted to the University of Bristol in April 2000).

Preferably, however, the bidentate ligands are prepared by a processwherein the phosphorus groups are introduced via a2-phospha-tricyclo[3.3.1.1{3,7}]decane group or a derivative thereof,instead of via an arylalkyl group having two primary phosphorus groups.

The preferred process for preparing the bidentate ligands comprisesthree synthetic steps.

In a first synthetic step an appropriate2-phosphatricyclo[3.3.1.1{3,7}]decane group or a derivative thereof isreacted with the hydride of a group 13 metal, including for example B,Al and Ga. Of these BH₃ is preferred. The first step reaction can becarried out at a wide range of temperatures. Suitably the temperaturelies within a range from −150° C. to 100° C. Preferably the reaction iscarried out at temperatures in the range for −50 to 50° C. and morepreferably from −10 to 10° C. Preferably the reaction is carried out ina solvent as stipulated below. The formed adduct is preferablyrecrystallised before use in the subsequent second step.

In a second subsequent synthetic step the group 13 adduct of the2-phospha-tricyclo[3.3.1.1{3,7}]decane group or a derivative thereof isreacted in a first sub-step with an alkylated group I A metal,preferably Na or Li, most preferably a lithium alkyl. The reaction canbe carried out at a temperature in the range from −150° C. to 100° C.,preferably carried out at a temperature in the range from −100° C. to 0°C., and more preferably a temperature from −80 to −50° C. The in-situprepared lithium phosphide is subsequently reacted in a second sub-stepwith an appropriate halogenated arylalkyl group of the formulaH-A¹-R-A²-H  (III)wherein H represents F, Cl, Br, I, and preferably Cl or Br; and A¹, A²and R represent groups as defined herein before.

The reaction can be carried out at a temperature in the range from −150°C. to 100° C. The reaction is preferably carried out at a temperaturebelow 0° C., preferably a temperature from −80 to −50° C. Preferably thereactions of the second synthetic step are carried out in a solvent asstipulated below.

In a third synthetic step the group 13 protecting group is removed fromthe bidentate diphosphine group 13 adduct. The removal of the group 13protecting group can conveniently be achieved directly after the secondsynthetic step by refluxing with an amine. Amines that can be usedinclude mono- or polyamines. Suitable examples include dialkyl andtrialkylamines wherein the alkyl groups preferably have in the rangefrom 1 to 6 carbon atoms, such as diethylamine, triethylamine,dimethylamine and trimethylamine; triarylamines such as triphenylamine;arylalkylamines such as diethylphenylamine and dimethylphenylamine; andcyclic structures containing nitrogen atoms such as1,4-diazabicyclo[2,2,2]octane. Of these dimethylamine and diethylamineare preferred. Diethylamine is especially preferred. The second andthird synthetic step are preferably carried without an intermediaterecrystallisation step. The reaction product of the third synthetic stepis subsequently preferably recrystallised before use as a bidentatediphosphine ligand.

All reaction steps are preferably carried out in a solvent. Examples ofsuitable solvents include saturated hydrocarbons such as, e.g.,paraffins and isoalkanes; ethers such as 2,5,8-trioxanonane (diglyme),diethylether, tetrahydrofuran and anisole; sulphones such as sulpholane,and aromatic hydrocarbons such as toluene. In the first synthetic stephalogenated saturated alkanes such as dichloromethane might also be usedas a solvent. A preferred solvent for all synthetic steps istetrahydrofuran.

As a source of anions, any compound generating these anions may be used.Suitably, acids, or salts thereof, are used as source of anions, forexample any of the acids mentioned above, which may also participate inthe salts of the group VIII metal.

Preferably acids are used as anion source having a pKa value of lessthan 6, more preferably less than 5, measured in aqueous solution at 18°C. Examples of suitable anions are anions of carboxylic acids;phosphoric acid; sulphuric acid; sulphonic acids, such asmethanesulphonic acid, trifluoromethanesulphoni-c acid,tert-butane-sulphonic acid, p-toluenesulphonic acid and2,4,6-trimethylbenzene-sulphonic acid; and halogenated carboxylic acidssuch as trifluoroacetic acid.

Also, complex anions are suitable, such as the anions generated by acombination of a Lewis acid such as BF₃, AlCl₃, SnF₂, Sn(CF₃SO₃)₂, SnCl₂or GeCl₂, with a protic acid, such as a sulphonic acid, e.g. CF₃SO₃H orCH₃SO₃H or a hydrohalogenic acid such as HF of HCl, or a combination ofa Lewis acid with an alcohol. Examples of such complex anions are BF₄—,SnCl₃—, [SnCl₂.CF₃SO₃]— and PF₆—.

Preferably the source of anions is a carboxylic acid. More preferably acarboxylic acid having a pKa of below 6, more preferably a carboxylicacid with a pKa in the range from 2 to 6 and most preferably acarboxylic acid with a pKa in the range from 4 to 6, measured in aqueoussolution at 18° C. Preferred carboxylic acids that can be used includecarboxylic acids with up to 15 carbon atoms, preferably with up to 10carbon atoms. Such carboxylic acids can be branched, linear or cyclicand can be saturated or non-saturated. Examples of suitable carboxylicacids include pentanoic acid, pivalic acid, propanoic acid and propenoicacid.

When the process according to the invention is used to prepare acarboxylic acid, this carboxylic acid is a preferred source of anions,such that the anions complexing with the group VIII metal are anions ofthe carboxylic acid. For example, the carbonylation of ethene withcarbon monoxide and water to prepare propanoic acid is advantageouslycarried out using propanoic acid as a source of anions. Preferablyessentially no anions of any additional acids “stronger” than thecarboxylic acid, i.e. acids having a pKa higher than that of thecarboxylic acid in the used solvent, are present.

In the process of the invention, the starting materials and the formedcarbonylation product can act as reaction diluent, but also anadditional (inert) solvent can be present. Examples of additionalsolvents include saturated hydrocarbons such as, e.g., paraffins andisoalkanes are recommended and furthermore ethers such as2,5,8-trioxanonane (diglyme), diethylether and anisole; sulphones suchas sulpholane, and aromatic hydrocarbons such as toluene.

In a preferred embodiment a carboxylic acid is used as a reactiondiluent. Preferably a carboxylic acid having a pKa of below 6, morepreferably a carboxylic acid with a pKa in the range from 2 to 6 andmost preferably a carboxylic acid with a pKa in the range from 4 to 6,measured in aqueous solution at 18° C. When the process according to theinvention is used to prepare a carboxylic acid, this carboxylic acid isa preferred reaction diluent. For example, the carbonylation of ethenewith carbon monoxide and water to prepare propanoic acid isadvantageously carried out in propanoic acid as a solvent.

Carbon monoxide partial pressures in the range of 1-65 bar arepreferred. The carbonylation reaction is conveniently carried out atmoderate temperatures. Accordingly, the process is suitably carried outat a temperature in the range of. 30 to 200° C., preferred temperaturesbeing in the range of 50 to 150° C. The reaction pressures may also varywidely. For instance, the reaction can be carried out with pressures inthe range of 1 to 100 bar, pressures in the range of 2 to 30 bar beingpreferred.

The ethylenically unsaturated compound and co-reactant are suitablysupplied in a molar ratio within the range of 10:1 to 1:10, preferablywithin the range of 5:1 to 1:5, more preferably within the range of 2:1to 1:2.

The quantity, in which the catalyst is used, is not critical and mayvary within wide limits. For practical reasons amounts in the range of10⁻⁸ to 10⁻¹, preferably in the range of 10⁻⁷ to 10⁻² mole atom of groupVIII metal per mole of unsaturated compound can be used.

For the preparation of the catalysts of the invention, the amount ofbidentate diphosphine ligand can be applied in some excess of the amountof the group VIII metal, expressed as moles of ligand per mole atom ofthe group VIII metal.

Preferably the amount of ligand is selected such that per mole atom ofthe group VIII metal 0.5 to 10 moles of ligand are present. Morepreferably the molar amount of bidentate diphoshine ligand per mole ofgroup VIII metal is in the range of 1 to 3, and most preferably in therange of 1 to 2. In the presence of oxygen, slightly higher amounts canbe beneficial.

The amount of the anion source may vary widely depending on whether thecarboxylic acid is simultaneously the reaction product or theco-reactant or simultaneously used as a solvent. For practical reasonsthe amount of source of anions is at least 0.5 moles per mole of groupVIII metal. Preferably the amount of source of anions varies in a rangefrom 0.5 to 10⁷, preferably from 1 to 10⁶ moles per mole of group VIIImetal.

The process according to the invention can be carried out batch-wise,semi-continuously and continuously. If the process is carried outsemi-continuously, appropriate additional amounts of carbon monoxideand/or ethylenically unsaturated compound and/or co-reactant arepreferably added intermittently at appropriate stages in the process.Preferably the process is carried out continuously.

The carbonylation product prepared in the process according to theinvention can be used in a wide range of applications. In an especiallypreferred embodiment the process according to the invention is used toprepare a carboxylic acid by carbonylation of an ethylenicallyunsaturated compound with carbon monoxide and water. The preparedcarboxylic acid can, in turn be used for the preparation of a carboxylicanhydride by carbonylation of an ethylenically unsaturated compound withcarbon monoxide using the carboxylic acid as a co-reactant.

The invention therefore also provides a process for the preparation of acarboxylic acid and its corresponding carboxylic anhydride comprising:

-   A) carbonylation of an ethylenically unsaturated compound with    carbon monoxide and water in the presence of a catalyst according to    the process as described herein, to yield an carboxylic acid;-   B) carbonylation of an ethylenically unsaturated compound with    carbon monoxide and the carboxylic acid obtained in step A) in the    presence of a catalyst, to yield an carboxylic anhydride.

The catalyst in step B) is preferably a catalyst comprising:

-   i) a source of group VIII metal;-   ii) a phosphorus containing ligand; and-   iii) a source of anions.

The source of group VIII metal i) is preferably a source of group VIIImetal as described hereinbefore.

The phosphorus containing ligand ii) is preferably a bidentatediphoshine. Preferred bidentate diphosphines include those described inWO-A-9842717 and WO-A-0172697 and those bidentate diphosphines describedhereinbefore. Especially preferred bidentate diphosphines include1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]decyl)propaneand1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl)-methylene-benzene(also sometimes referred to as1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]decyl)-ortho-xylene).

The source of anions iii) is preferably a source of anions as describedherein before. The carboxylic acid as prepared in step A) is especiallypreferred as a source of anions. In a preferred embodiment essentiallyno anions of any additional acids “stronger” than the carboxylic acid,i.e. acids having a pKa higher than that of the catboxylic acid in theused solvent, are present.

The ethylenically unsaturated compound in step A) or in step B) canindependently be any of the ethylenically unsaturated compoundsmentioned herein before. The ethylenically unsaturated compound in stepA) and step B) can be the same or different.

If the ethylenically unsaturated compound in step A) and B) are thesame, a symmetrical carboxylic anhydride is advantageously obtained instep B).

In an especially preferred embodiment the ethylenically unsaturatedcompound in step A) and in step B) is ethene. In this case propanoicacid and propanoic anhydride are obtained at high reaction rates and ingood selectivity.

The ethylenically unsaturated compound in step A) and B) can also bechosen such that a specific asymmetrical carboxylic anhydride isobtained in step B).

Reaction conditions for step B), e.g. temperature and pressure, arepreferably as described herein before for step A).

The process steps A) and B) can be carried out in a wide range ofsolvents, including the ones mentioned herein before. Preferably stepsA) and B) are carried out in the same solvent and most preferably thesolvent in both step A) and step B) is the carboxylic acid as preparedin step A).

The present invention advantageously allows steps A) and B) to becarried out simultaneously, for example in one reactor. In such aprocess carboxylic anhydride can advantageously be prepared at high rateand with good selectivity using as starting compounds an ethylenicallyunsaturated compound, carbon monoxide and water.

An carboxylic anhydride prepared by this process can be used for variousapplications. In a preferred application the carboxylic anhydride isused as an acylation agent. The carboxylic anhydride can for example beused in the acylation of aromatic alcohols such as for example phenol toprepare the corresponding carboxylic ester. Another example is theacylation of amines or amides to respectively amides or imides. Byacylation of diamines such as ethylene diamine and propylene diamine,bleach activators such as respectively tetra acetyl ethylene diamine andtetra acetyl propylene diamine can be prepared.

The prepared carboxylic anhydride can also react with acetic acid in aequilibrium reaction to prepare acetic anhydride, a compound which isotherwise difficult to obtain.

The invention will now be illustrated by the following non-limitingexamples.

COMPARATIVE EXAMPLE A

An autoclave was charged 50 ml propionic acid, 5 ml water, 0.1 mmolPd(OAc)₂ and 0.15 mmol1,3-PP′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl)propane. After being flushed, the autoclave was next pressurized with apartial pressure of 15 bar carbon monoxide and 10 bar ethene. Followingsealing of the autoclave, its contents were heated to a temperature of100° C. and maintained at that temperature for 1.5 hours. After cooling,a sample was taken from the contents of the autoclave and analysed byGas Liquid Chromatography. The average rate of the reaction, expressedas mol product per mol Pd per hour, was also calculated. The averagerate of reaction is defined as the mean rate of carbon monoxideconsumption during a period up to exhaustion of either one of ethene orcarbon monoxide.

Ethene was fully converted with 100% selectivity into propionic acid atan average rate of 2500 mol per mol Pd per hour (mol/mol.hr). Theaverage rate of reaction was defined as the mean rate of carbon monoxideconsumption during a period up to the exhaustion of either one of etheneor carbon monoxide.

EXAMPLE 1

Comparative example A was repeated, however using 0.15 mmol1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}decyl)-methylene-benzeneinstead of 0.15 mmol1,3-PP′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]-decyl)propane and using 10 bar instead of 15 bar carbon monoxide. Theautoclave was cooled after 1 hour.

Ethene was fully converted with 100% selectivity into propionic acid atan average rate of 10000 mol/mol.hr.

COMPARATIVE EXAMPLE B

Example 1 was repeated, however using 0.15 mmol1,2-bis(di-t-butylphosphino)-methylene-benzene, instead of 0.15 mmol1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}decyl)-o-xylene.The autoclave was cooled after 5 hours.

Ethene was converted with 100% selectivity into propionic acid at anaverage rate of 800 mol/mol.hr.

EXAMPLE 2 Semi-Continuous

Example 1 was repeated, however-using 32 ml instead of 5 ml water and 20bar of an 1:1 gas mixture of ethene and carbon monoxide. The gas mixturewas introduced to the autoclave 30 times in portions of 5-15 bar over 2hours at a process temperature of 100° C.

Ethene/CO were fully converted with 100% selectivity into propionic acidat an average rate of 10000 mol/mol.hr.

EXAMPLE 3

An autoclave was charged with 15 ml methyl-3-pentenoate and 40 mltoluene as a solvent, 0.1 mmol rhodium dicarbonyl acetylacetonate and0.15 mmol1,2-PP′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]decyl)-methylene-benzene.After being flushed, the autoclave was next pressurized with a partialpressure of 30 bar carbon monoxide and 30 bar hydrogen. Followingsealing of the autoclave, its contents were heated to a temperature of100° C. and maintained at that temperature for 1 hour. After cooling, asample was taken from the contents of the autoclave and analysed by GasLiquid Chromatography. Conversion of methyl-3 pentenoate was 100%. Theselectivity towards 2-formyl methyl pentanoate was 3,5%, 3-formyl methylpentanoate 51.3%, 4 formyl methyl pentanoate 39.4% and 5 formylpentanoate 4.0%. The average rate of conversion towards these productswas 2500 mol per mol Rh per hour (mol/mol.hr).

EXAMPLE 4 Synthesis of1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}decyl)-methylene-benzene)

Synthesis Step 1:

To a solution of2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]decanehydride (H-PA) (13 g, 60 mmol) in tetrahydrofuran (40 ml) was added a 1Msolution of Boron trihydride (73 mmol) in tetrahydrofuran over 5 min at0° C. After 4 h stirring at room temperature (20° C.), the solvent wasremoved and the crude product was recrystallised from the minimum volumehot tetrahydrofuran (20 ml) and washed with hexane (2×5 ml) to afford2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]decaneborane (H-PA.BH₃) as colourless crystals. Further product was obtainedby recrystallisation of the filtrate from hot tetrahydrofuran (7 ml).The yield of H-PA.BH₃ was 86% based on H-PA.

Synthesis Step 2:

To a solution of H-PA.BH₃ (3.67 g, 16 mmol) in tetrahydrofuran (40 ml)was added hexyllithium (6.4 ml (2.5 M), 16 mmol) at −75° C. Afterstirring for 1 h, α,α′-dibromo-o-xylene (2.1 g, 8 mmol) intetrahydrofuran (20 ml) was added at −75° C. and the reaction allowed towarm to room temperature. After 3 hours, diethylamine (3 ml, 28 mmol)was added and the reaction refluxed for 2 hours. After cooling, thesolvent was removed and the crude product dissolved in toluene (60 ml)and washed with water (4×40 ml). The solvent was removed to afford1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]decyl)-methylene-benzene(3.9 g, 91%) as a white solid (see thesis by Robert Pugh submitted tothe University of Bristol in April 2000 for NMR characterization). Thediphosphine may be further purified by recrystallisation from methanol.

1. A process for the carbonylation of an ethylenically unsaturatedcompound with carbon monoxide and a co-reactant in the presence of acatalyst comprising: a) a source of a group VIII metal; b) a bidentatediphosphine of formula I,

wherein R¹ represents a bivalent radical that together with thephosphorus atom to which it is attached is an optionally substituted2-phospha-tricyclo[3.3.1.1 {3,7}]-decyl group or a derivative thereof inwhich one or more of the carbon atoms are replaced by heteroatoms(“2-PA” group); wherein R² and R³ independently represent univalentradicals of up to 20 atoms or jointly form a bivalent radical of up to20 atoms; and wherein A¹ and A² independently represent optionallysubstituted alkylene groups and R represents an optionally substitutedaromatic group; and, c) a source of anions.
 2. A catalyst comprising: a)a source of palladium or rhodium; b) a bidentate diphosphine of formulaI,

wherein R¹ represents a bivalent radical that together with thephosphorus atom to which it is attached is an optionally substituted2-phospha-tricyclo[3.3.1.1 {3,7}]-decyl group or a derivative thereof inwhich one or more of the carbon atoms are replaced by heteroatoms(“2-PA” group); wherein R² and R³ independently represent univalentradicals of up to 20 atoms or jointly form a bivalent radical of up to20 atoms; and wherein A¹ and A² independently represent optionallysubstituted alkylene groups and R represents an optionally substitutedaromatic group; and, c) a source of anions.
 3. The catalyst of claim 2wherein R² and R³ together with the phosphorus atom form a 2-PA groupidentical to R¹.
 4. The catalyst of claim 3 wherein the bidentatediphosphine is1,2-P,P′-[di-(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}decyl)-methylene]-benzene.5. The catalyst of claim 2 wherein the source of anions is a carboxylicacid.
 6. The process of claim 1 wherein the catalyst is a catalystcomprising: a) a source of palladium or rhodium; b) a bidentatediphosphine of formula I,

wherein R¹ represents a bivalent radical that together with thephosphorus atom to which it is attached is an optionally substituted2-phospha-triyclo[3.3.1.1 {3,7}]-decyl group or a derivative thereof inwhich one or more of the carbon atoms are replaced by heteroatoms(“2-PA” group): wherein R² and R³ independently represent univalentradicals of up to 20 atoms or jointly form a bivalent radical of up to20 atoms; and wherein A¹ and A² independently represent optionallysubstituted alkylene groups and R represents an optionally substitutedaromatic group; and, c) a source of anions.
 7. The process of claim 1wherein a carboxylic acid is used as a reaction diluent.
 8. The processfor the preparation of a carboxylic acid and its correspondingcarboxylic anhydride of claim 1 comprising the following steps: a) ofcarbonylation of an ethylenically unsaturated compound with carbonmonoxide and water to yield a carboxylic acid; and, b) of carbonylationof an ethylenically unsaturated compound with carbon monoxide and thecarboxylic acid obtained in step a) in the presence of a catalyst toyield a carboxylic anhydride.
 9. The process of claim 8 wherein thecatalyst in step b) is a catalyst comprising: i) a source of group VIIImetal; ii) a phosphorus containing ligand; and iii) a source of anions.10. The process of claim 9 wherein the source of anions iii) is thecarboxylic acid prepared in step a).
 11. The process of claim 8 whereinthe carboxylic acid as prepared in step a) is used as a reaction diluentin both step a) and step b).